Collarless circularly magnetized torque transducer having two phase shaft and method for measuring torque using same

Abstract

A magnetoelastic torque sensor for providing an output signal indicative of the torque applied to a member about an axially extending axis of the member, comprising, a member which is unitary and of generally homogeneous chemical composition, the member comprising separate magnetically active and magnetically substantially passive regions. A first magnetoelastically active region in the member is magnetically polarized in a single circumferential direction and possesses sufficient magnetic anisotropy to return the magnetization in the region, following the application of torque to the member, to the single circumferential direction when the applied torque is reduced to zero, whereby the magnetoelastically active region produces a magnetic field varying with the torque. Magnetic field sensors are mounted proximate to the magnetoelastically active region and oriented with respect thereto to sense the magnitude of the magnetic field at the sensors and provide the output signal in response thereto. The magnetoelastically active region of the member is formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90° quadrant symmetrically disposed around the single circular direction and has a coercivity sufficiently high to prevent irreversible loss of the magnitude of the circumferential polarization.

What is claimed is: 
     
       1. A magnetoelastic torque sensor for providing an output signal indicative of the torque applied to a member about an axially extending axis of said member, comprising: a member which is unitary and of generally homogeneous chemical composition throughout, said member comprising separate magnetically active and magnetically substantially passive regions;   a first magnetoelastically active region in said member, said region being magnetically polarized in a single circumferential direction and possessing sufficient magnetic anisotropy to return the magnetization in said region, following the application of torque to said member, to said single cirumferential direction when the applied torque is reduced to zero, whereby said magnetoelastically active region produces a magnetic field varying with said torque;   magnetic field sensor means mounted proximate to said magnetoelastically active region and oriented with respect thereto to sense the magnitude of the magnetic field at said sensor means and provide said output signal in response thereto;   said magnetoelastically active region of said member being formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90° quadrant symmetrically disposed around said single circular direction and having a coercivity sufficiently high to prevent irreversible loss of the magnitude of the circumferential polarization.   
     
     
       2. A magnetoelastic torque sensor, as claimed in claim 1, wherein said magnetically active regions comprise a first metallurgical phase and said magnetically substantially passive regions comprise at least one metallurgical phase other than said first metallurgical phase. 
     
     
       3. A magnetoelastic torque sensor, as claimed in claim 2, wherein said first metallurgical phase is sufficiently ferromagnetic and magnetostrictive to fulfill the requirements of a magnetically active region and said at least one metallurgical phase exhibits sufficiently low permeability to fulfill the requirements of a substantially passive region. 
     
     
       4. A magnetoelastic torque sensor, as claimed in claim 3, wherein said member is formed of a predominantly iron containing alloyed steel, said magnetically active regions comprise a martensitic phase and said magnetically substantially passive regions comprise an austenitic phase. 
     
     
       5. A magnetoelastic torque sensor, as claimed in claim 3, wherein said member is formed of a steel selected from the group consisting of Hadfield steels, TRIP steels, 18-8 stainless steels and precipitation hardening stainless steels containing chromium and nickel. 
     
     
       6. A magnetoelastic torque sensor, as claimed in claim 1, including at least one additional axially distinct, circumferential magnetoelastically active region which is magnetically contiguous with said first region, each additional region being polarized in a circumferential direction opposite to the polarization direction of magnetically contiguous magnetoelastically active regions. 
     
     
       7. A magnetoelastic torque sensor, as claimed in claim 1, wherein said active regions of said member are formed of a polycrystalline material having cubic symmetry. 
     
     
       8. A magnetoelastic torque sensor, as claimed in claim 1, wherein said member is a solid, elongated shaft. 
     
     
       9. A magnetoelastic torque sensor, as claimed in claim 1, wherein said member is a hollow, elongated shaft. 
     
     
       10. A magnetoelastic torque sensor, as claimed in claim 1, wherein said member is an elongated shaft having an axially extending enlarged diameter portion intermediate its ends and said magnetoelastically active region is formed on said enlarged diameter portion. 
     
     
       11. A magnetoelastic torque sensor, as claimed in claim 1, wherein said member is an elongated shaft having an axially extending reduced diameter portion intermediate its end portions and said magnetoelastically active region is formed on said reduced diameter portion. 
     
     
       12. A magnetoelastic torque sensor, as claimed in claim 11, wherein said reduced diameter portion is a separate shaft which is rigidly attached to the larger diameter end portions. 
     
     
       13. A magnetoelastic torque sensor, as claimed in claim 1, wherein the coercivity of said member is greater than 15 Oe. 
     
     
       14. A magnetoelastic torque sensor, as claimed in claim 1, wherein the coercivity of said member is greater than 20 Oe. 
     
     
       15. A magnetoelastic torque sensor, as claimed in claim 1, wherein the coercivity of said member is greater than 35 Oe. 
     
     
       16. A magnetoelastic torque sensor, as claimed in claim 1, wherein said magnetic field sensor means comprises a solid state sensor. 
     
     
       17. A magnetoelastic torque sensor, as claimed in claim 16, wherein said magnetic field sensor means comprises a Hall-effect sensor. 
     
     
       18. A magnetoelastic torque sensor, as claimed in claim 1, wherein said magnetic field sensor means is mounted and oriented with respect to said magnetoelastically active region to sense the polarity of said magnetic field. 
     
     
       19. A magnetoelastic torque sensor, as claimed in claim 18, wherein said magnetic field sensor means is mounted in a fixed position proximate to said magnetoelastically active region. 
     
     
       20. A magnetoelastic torque sensor, as claimed in claim 18, wherein said sensor means is positioned proximate an end of said region. 
     
     
       21. A magnetoelastic torque sensor, as claimed in claim 18, wherein said sensor means comprises at least two sensors, at least one sensor being positioned proximate each end of said region. 
     
     
       22. A magnetoelastic torque sensor, as claimed in claim 1, wherein said magnetoelastically active region has, in the absence of torque applied to said member, a circumferential magnetic orientation having no net magnetization component in the axial direction. 
     
     
       23. A magnetoelastic torque sensor, as claimed in claim 22, wherein said magnetoelastically active region has, when torque is applied to said member, a helical magnetic orientation having both circumferential and axial components, said magnetic field sensor means being positioned and oriented for sensing the magnetic field arising from said axial components of magnetization. 
     
     
       24. A method of sensing a torque applied to a torqued member extending in an axial direction, comprising the steps of: (a) providing a member which is unitary and of generally homogeneous chemical composition throughout, said member comprising separate magnetically active and magnetically substantially passive regions, a first magnetoelastically active region in said member, said region being magnetically polarized in a single circumferential direction and possessing sufficient magnetic anisotropy to return the magnetization in said region, following the application of torque to said member, to said single cirumferential direction when the applied torque is reduced to zero, at least said magnetoelastically active region of said member being formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90° quadrant symmetrically disposed around said single circular direction and having a coercivity sufficiently high to prevent irreversible loss of the magnitude of the circumferential polarization;   (b) producing a magnetic field as a consequence of the application of torque to said member; and   (c) sensing the magnitude of the magnetic field at a position proximate to said magnetoelastically active region as an indication of the magnitude of the torque applied to said member.   
     
     
       25. A method, as claimed in claim 24, wherein said magnetically active regions comprise a first metallurgical phase and said magnetically substantially passive regions comprise at least one metallurgical phase other than said first metallurgical phase. 
     
     
       26. A method, as claimed in claim 25, wherein said first metallurgical phase is sufficiently ferromagnetic and magnetostrictive to fulfill the requirements of a magnetically active region and said at least one metallurgical phase exhibits sufficiently low permeability to fulfill the requirements of a substantially passive region. 
     
     
       27. A magnetoelastic torque sensor, as claimed in claim 26, wherein said member is formed of a predominantly iron containing alloyed steel, said magnetically active regions comprise a martensitic phase and said magnetically substantially passive regions comprise an austenitic phase. 
     
     
       28. A method, as claimed in claim 24, wherein the application of torque to said member causes said magnetoelastically active region to have a helical magnetic orientation with both circumferential and axial magnetization components and said sensing step comprises sensing the magnetic field arising from said axial components of said magnetization. 
     
     
       29. A method, as claimed in claim 24, including the step of providing at least one additional axially distinct, circumferential magnetoelastically active region which is magnetically contiguous with said first region, each additional region being polarized in a circumferential direction which is opposite from the polarization direction of magnetically contiguous magnetoelastically active regions. 
     
     
       30. A method, as claimed in claim 24, wherein said member is formed of a polycrystalline material having cubic symmetry. 
     
     
       31. A method, as claimed in claim 24, wherein the coercivity of said magnetoelastically active region is greater than 15. 
     
     
       32. A method, as claimed in claim 24, wherein the sensing step is accomplished at least in part by positioning a magnetic field sensing device proximate to and spaced from said magnetoelastically active region. 
     
     
       33. A method of producing a magnetoelastic torque transducer from a member to which an axial torque is applied for producing a magnetic field varying with said torque, the magnitude of said magnetic field being sensed by magnetic field sensors for providing an output signal indicative of the applied torque, comprising the steps of: (a) providing a ferromagnetic, magnetostrictive unitary member which is of generally homogeneous chemical composition throughout;   (b) inducing phase transformations in said member by processes selected from the group consisting of thermal processes, mechanical processes and combinations thereof for defining in said member separate magnetically active and magnetically substantially passive regions; and   (c) polarizing a finite axial extent of a first magnetoelastically active region in a magnetizing field in a single circumferential direction, said region possessing sufficient magnetic anisotropy to return the magnetization in said region, following the application of torque to said member, to said single circumferential direction when the applied torque is reduced to zero;   (d) said member being formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90° quadrant symmetrically disposed around said single circmferential direction and having a coercivity sufficiently high to prevent irreversible loss of the magnitude of the circumferential polarization.   
     
     
       34. A method, as claimed in claim 33, wherein said magnetically active regions comprise a first metallurgical phase and said magnetically substantially passive regions comprise at least one metallurgical phase other than said first metallurgical phase. 
     
     
       35. A method, as claimed in claim 34, wherein said first metallurgical phase is sufficiently ferromagnetic and magnetostrictive to fulfill the requirements of a magnetically active region and said at least one metallurgical phase exhibits sufficiently low permeability to fulfill the requirements of a substantially passive region. 
     
     
       36. A method, as claimed in claim 35, wherein said member is formed of a predominantly iron containing alloyed steel, said magnetically active regions comprise a martensitic phase and said magnetically substantially passive regions comprise an austenitic phase. 
     
     
       37. A method, as claimed in claim 33, wherein said member has a longitudinal axis and said magnetic polarization is achieved by rotating said transducer thereabout while being subjected to the magnetizing field near two opposite magnetic poles.